Method of environmentally protecting a pipeline

ABSTRACT

A method of covering a joint between pipelines comprises installing a heat recoverable polymer sheet coated on its inner surface with a hot-melt adhesive comprising a mixture of 25 to 40 parts by weight of a polyethylene alkyl acrylate terpolymer containing maleic anhydride and having a melt flow index as determined according to ASTM D1238-70 of at least 40, and 25 to 70 parts by weight of a polyethylene alkyl acrylate copolymer having a melt flow index as determined according to ASTM D1238-70 of at least 40.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to coverings for pipelines, and inparticular to coverings which comprise a heat recoverable sheet or tapecoated on its inner surface with a hot-melt adhesive comprising a blendof polyethylene alkyl acrylates, particularly for covering pre-polymericcoated or thermally insulated pipelines, or where the heat recoverablebacking is a tape, for helically wrapping around bare metal pipe, orpolymeric coating of a thermally insulated pipe.

2. Introduction to the Invention

Heat recoverable articles are well known. They are articles thedimensional configuration of which may be made substantially to changewhen subjected to heat treatment.

Usually these articles recover, on heating, towards an original shapefrom which they have previously been deformed but the term "heatrecoverable" as used herein, also includes an article, which, onheating, adopts a new configuration, even if it has not been previouslydeformed. Examples of such heat recoverable articles based on polymericsheet material are found in U.S. Pat. Nos. 2,027,962, 3,086,242, and3,597,372. Heat recoverable articles based on fabrics are also known.Typically these comprise a recoverable fabric in conjunction with apolymeric matrix formed by laminating a polymeric material to one orboth sides of the fabric to render it impervious. Examples are describedin European Patent Publication Nos. 116,393, 117,026, and 116,392.

The use of a polyethylene alkyl acrylate on a heat recoverable sleevefor environmental protection, particularly of a cable splice, isdescribed in European Patent Publication No. 330,480, which is thecounterpart of U.S. Pat. No. 4,965,320. The entire disclosure of U.S.Pat. No. 4,965,320 is incorporated herein by reference.

SUMMARY OF THE INVENTION

The present invention provides particular methods of applying arecoverable sheet or tape coated with the specified hot-melt adhesivearound pipelines.

A first aspect of the invention provides a method of environmentallyprotecting a polymer-coated metal pipeline, or a joint between two suchpipelines where the pipelines have been bared of polymer coating at thejoint region, the method comprising:

(i) positioning a heat recoverable sheet which is coated on one surfacethereof with a hot melt adhesive composition, such that the adhesivefaces the pipeline, and such that the adhesive-coated sheet at leastoverlaps the polymer coating, the adhesive comprising a mixture of 25 to40 parts by weight of a polyethylene alkyl acrylate terpolymercontaining maleic anhydride and having a melt flow index as determinedaccording to ASTM D1238-70 of at least 40, and 25 to 70 parts by weightof a polyethylene alkyl acrylate copolymer having a melt flow index asdetermined according to ASTM D1238-70 of at least 40; and

(ii) applying sufficient heat to recover the sheet and to activate theadhesive.

DETAILED DESCRIPTION OF THE INVENTION

The heat-recoverable sheet which is preferably shrinkable may betubular, i.e. of closed cross-section, or may be wraparound, that is itmay be in the form of a sheet wrapped around the pipelines, such thatlongitudinal edges thereof abut or overlap. The longitudinal edges maybe held in position relative to each by any of a number of known closuremechanisms, e.g. a polymeric patch may be bonded to overlapped edges ofthe wraparound, or a penetrating closure e.g. stitching or riveting, canbe used, or the overlapped edges may simply be bonded or fused to eachother.

One particular application of the first aspect of the present inventionis for covering a joint, e.g. a weld between two metal pipes coated witha corrosion protection layer. As an example steel or other metal pipesare often pre-coated in the factory with a polyethylene coating. Thiscoating may be so-called "three-layer-PE coating". The polyethylenecoating is typically extruded. As another example a coating comprisingsintered polyethylene maybe used. In order to join such pipes they areusually bared of coating at their ends, and then welded. In order toprotect the joint it is therefore necessary to make good the coating inthe joint region.

A number of solutions to the above problem have been suggested,including the application of a heat shrinkable sheet precoated with aheat-activatable adhesive.

For any heat-activatable adhesives there is generally a range ofso-called "service temperatures" specified. This range defines thetemperatures between which the adhesive retains its adhesive bondingpower. At higher temperatures, it will have insufficient viscosity tomaintain the bond under the influence of the external (mainly shear andcreep) forces that are exerted by the pipeline environment, and at lowertemperatures it may become brittle. Typical heat-activatable adhesive,e.g. polyethylene copolymer based adhesives, typically, require themetal pipes to be heated at least 60° C. above the maximum servicetemperature specified in order properly to activate them. In thiscontext the maximum service temperature is defined as the highesttemperature at which the adhesive maintains its bond to the substrateand does not show onset of movement when subjected to a static shearcreep force of 2.50-2.75 N/cm². Where the adhesive is to be applied on asheet to a metal pipeline, this practically means that significantpre-heat needs to be applied to the pipeline in order to activate theadhesive. Indeed in some cases, e.g. where the pipelines is acting as asignificant heat sink, e.g. if carrying fluid such as oil, it may not bepossible to reach the activation temperature at all. Preheating ofpipelines is typically achieved by applying a gas-torch for severalminutes. This is both time consuming and difficult, particularly if inconstrained surroundings. Also where the pipeline is precoated with apolymer coating this may be damaged by the pre-heating. We have foundthat the particular adhesive used in the present invention isparticularly advantageous for applying to pipelines since it may beactivated by heating the pipeline to temperatures of at most 40° C., oreven at most 35° C. or 30° C. above the specified maximum servicetemperature (as hereinbefore defined), i.e. to lower temperatures thanused hitherto. This substantially reduces the amount of preheatingneeded, and reduces time and minimises possible damage to any existingpolymeric coating on the pipelines.

Thus where the invention according to the first aspect of the inventionis used to protect a joint between two such coated pipelines bared ofcoating in the welded joint region, the sheet is positioned to cover thejoin and to overlap the remaining coating on either side of the join.The relatively low temperature needed to activate the adhesive(compared, for example, to polyethylene copolymer based hot-meltadhesives) means that the adhesive coated sleeve can be applied withoutdamage to the pre-existing polymer coating on either side of the join.

In a similar way, according to the first aspect of the invention, theadhesive coated sheet can be installed over an individual pre-coatedpipeline, rather than over a joint. This may be desirable, for example,to repair damage such as a hole in the polymer coating.

Similarly the method according to the first aspect of the invention canbe used to protect thermally insulated pipelines, such as districtheating pipelines, or joints there-between. Such pipelines are typicallymetal, e.g. steel, with a thick polyurethane coating and an outerpolyethylene jacket.

This invention is also concerned with covering and protecting barepipelines.

A second aspect of the present invention provides a method of covering(a) a bare metal pipeline, or (b) a polymer coated pipeline, or a jointbetween such pipelines where the pipelines have been bared of insulationin the joint region, the method comprising

(i) helically wrapping a heat recoverable tape around the pipeline orinsulation, the tape being coated on the inward facing surface with anadhesive comprising a mixture of 25 to 40 parts by weight of apolyethylene alkyl acrylate terpolymer containing maleic anhydride andhaving a melt flow index as determined according to ASTM D1238-70 of atleast 40, and 25 to 70 parts by weight of a polyethylene alkyl acrylatecopolymer having a melt flow index as determined according to ASTMD1238-70 of at least 40; and

(ii) applying heat to recover the tape into close conformity with thepipeline and to activate the adhesive.

The tape is preferably heat shrinkable. It may be applied as before topre-polymer coated pipelines, e.g. polyethylene coated pipelines, orthermally insulated pipelines, or to joints therebetween. As before theadvantages of relatively low activation temperature, and consequentminimizing of damage to the preexisting coating is apparent.Alternatively the tape may be applied to bare pipe, e.g. to bare metalpipeline such as steel. Where it is applied directly to bare pipelinethere is the advantage that it reduces the amount of preheat required.Indeed in some cases, e.g. where the pipeline is carrying oil or otherfluid and is acting as a significant heat sink the lower activationtemperature makes it possible to achieve activation, and therefore to beable to use an adhesive bonded polymer backing system. With previousheat activatable adhesives, e.g. hot melt polyethylene copolymer basedadhesives, it was not always possible to even reach activation incertain circumstances, e.g. where the pipeline was acting as a heatsink,and therefore other systems were devised, e.g. based on epoxy primer incombination with a heat shrinkable sleeve, for example as described inEuropean Patent Publication No. 181,233, which is the counterpart ofU.S. Pat. No. 4,732,632. The adhesive described in the present inventionmay be combined with the epoxy technology and heat shrinkable sleevedescribed in U.S. Pat. No. 4,732,632, the entire disclosure of which isincorporated herein by reference.

The tape may be helically wrapped so that the edges abut or overlap.Overlap may be any suitable amount, e.g. 10%, 20%, 50%.

A number of aspects are now described which are applicable to both thefirst and the second aspect of the invention.

The terpolymer (a) is preferably a terpolymer of ethylene, ethyl and/orbutyl (preferably ethyl) acrylate and maleic anhydride; and thecopolymer (b) is preferably a copolymer of ethylene and ethyl and/orbutyl (preferably butyl) acrylate. Other alkyl acrylates, particularlylower (especially C1-6, typically C2-5) acrylates may, however, be used.

The copolymer (b) consists essentially of ethylene and one or more(preferably one) alkyl acrylate, there preferably being no thirdcomonomer present. Any third comonomer is preferably present as lessthan 5 mole %, more preferably less than 2 mole %, especially less than1 mole %. Similarly, the terpolymer preferably consists essentially ofthe three specified monomers, any fourth preferably being present asless than 5 mole %, more preferably less than 2 mole %, especially lessthan 1 mole %.

In the present invention the adhesive composition is supplied as acoating on a heat-recoverable article. The heat-recoverable article maycomprise an extended continuum, or it may comprise a composite material,for example one shrinkable by virtue of a shrinkable fiber componentthereof. Preferred composite materials comprise shrinkable fibers and apolyethylene matrix material to which the adhesive composition isbonded.

As mentioned above the composite or other recoverable article may be inthe form of a tubular or wraparound sleeve or in the form of a tape.

The composition of the invention may additionally comprise aflow-temperature- or viscosity-modifying agent. Examples includetackifiers, waxes, modified waxes, polyisobutylene and that known by theMonsanto trade mark, Santicizer (e.g. N-ethyl o- and p-toluenesulphonamides) and equivalents. In general, ingredients that increaseviscosity are preferably avoided. Furthermore, the composition ispreferably not subjected to cross-linking, particularly if notirradiated. The term "tackifier" is used in the adhesives art to mean amaterial which when added to an adhesive promotes its adhesion to asubstrate, by increasing its ability to wet the substrate. Examples oftackifiers include low molecular weight polymers of monomers thatcontain ethylenic unsaturation and are free of polar groups. Specificexamples include Nevpene 9500 (trade mark) which is believed to be acopolymer of a mixture of aromatically- and aliphatically-substitutedethylene, and Piccotex 75 (trade mark of Industrial Chemical Corp.)which is believed to be a copolymer of vinyl toluene andalpha-methylstyrene. Preferred tackifiers, however, comprise terpenephenolic resins such as SP 553 (trade mark, Schenectady Corp.) andNevillac Hard (trade mark of Neville), particularly the former. Thetackifier preferably has a Brookfield viscosity at 160° C. of 80-1500centipoises; a ring-and-ball softening point as determined according toASTM E-28 of 50°-130° C. more preferably 80°-120° C., or preferably110°-120° C., particularly about 115° C.; and a molecular weight of lessthan 3000.

Given the basic components of the composition of the invention, theskilled man after reading this specification will be able to choose atackifier or other flow-temperature- or viscosity-modifying agent toachieve the desired properties, namely one or more of:

(a) a ring-and-ball softening point as determined according to ASTM E-28of from 90°-110° C., preferably 95°-105° C.;

(b) a viscosity as determined according to ASTM D3236 at 160° C. of from40-110 Pa.s., preferably 60-90 Pa.s.;

(c) a viscosity as determined according to ASTM D3236 at 200° C. of from10-50 Pa.s, preferably 15-40 Pa.s., more preferably 20-35 Pa.s., and aviscosity as determined according to ASTM D3236 at 160° C. of from40-110 Pa.s.

(d) an impact brittleness as determined according to ISO 974 of lessthan -30° C., preferably less than -35° C.; and

(e) a peel strength to non-flame-brushed and/or flame-brushedpolyethylene as determined according to DIN 30672 of greater than 30N/cm, preferably greater than 40 N/cm, especially greater than 50 N/cm.

It has been found that all of these properties can be achieved using theabove defined mixture of polyethylene alkyl acrylates, each of high meltflow index, together with from 5-15, preferably 10-15, parts by weightof SP 553 or equivalent as tackifier or other flow-temperature orviscosity-modifying agent. The use of alternative tackifiers oralternative quantities will in general allow chosen ones of the aboveproperties to be achieved.

The preferred viscosity achieved, optionally with the addition oftackifiers, is particularly advantageous for achieving good flow andfilling of any surface irregularities between the recoverable sheet ortape and the underlying pipe, or polymer coating on the pipe.

The adhesive used in the invention also has good high temperatureperformance, e.g. good peel strength even at high temperatures. Thiscombination of appropriate viscosity and good performance at highservice temperatures is a particular advantage of the present invention.

For some purposes it may be desirable to add small quantities of one ormore polyamides to the mixture. A suitable polyamide is one having anamine number below 5, preferably below 4. For example up to 15 parts byweight of a polyamide may be added, although it has been found thatsatisfactory properties can be achieved at lower cost with less than 5parts by weight of, and preferably substantially without, polyamide.

The adhesive used in the present invention preferably consistsessentially of the terpolymer, the copolymer, a tackifier and optionallya polyamide. The adhesive composition preferably contains substantiallyno polyamide, and no vinyl acetate nor copolymer thereof.

It is also preferred that the polyethylene alkyl acrylate terpolymer hasa melt flow index as defined of at least 70, more preferably from100-300. This terpolymer may, for example, comprise: a terpolymer ofethylene; ethyl acrylate and/or butyl acrylate (preferably ethylacrylate); and maleic anhydride. It preferably has a ring-and-ballsoftening point as determined according to ASTM E-28 of 80°-125° C.,more preferably 95°-120° C. Its viscosity as determined according toASTM D3236 at 160° C. is preferably from 120-140 Pa.s. Preferredterpolymers include that known by the trade mark Lotader 8200 (Orkem),and equivalents.

The polyethylene alkyl acrylate copolymer preferably has a melt flowindex as defined of at least 70, more preferably 100-300. It preferablyhas a ring-and-ball softening point as determined according to ASTM E28of 80°-125° C., more preferably 90°-115° C. Its viscosity as determinedaccording to ASTM D3236 at 160° C. is preferably from 70-150 Pa.s.Preferred copolymers include polyethylene butyl acrylates such as thatknown by the trade mark Lotryl 8600 (Orkem), and equivalents, andpolyethylene ethyl acrylates such as those known by the trade marksAlathon 704 (Dupont) and EA 89821 (USI), and equivalents.

The composition preferably has:

(a) 28-38 parts by weight of the polyethylene alkyl acrylate terpolymer;and

(b) 55-70 parts by weight of said polyethylene alkyl acrylate copolymer.

It is also preferred that the composition consist essentially of thepolyethylene alkyl (preferably ethyl) acrylate terpolymer, thepolyethylene alkyl (preferably butyl) acrylate copolymer, the tackifierand optionally, the polyamide. Preferably any other component is presentas less than 10 parts by weight, more preferably less than 5 parts byweight, especially less than 2 parts by weight. Examples of permissibleminor components include stabilizers such as antioxidants, a preferredamount of which is about 1 part by weight. Another permissible minorcomponent is carbon black. In particular the composition preferablycontains substantially no vinyl acetate nor copolymer thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample, with reference to the accompanying drawings, wherein:

FIG. 1 shows reinsulation of a joint between two polymer coatedpipelines bared of insulation in the joint region, using a methodaccording to the invention; and

FIG. 2 shows application of a heat shrinkable tape to a bare pipelineusing a method according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings. In FIG. 1, two steel pipelines are welded at4. Each is coated with an extruded coating of polyethylene 6. Thecoating has been removed in the region of weld 4. The pipeline ispreheated to a temperature about 40° C. higher than the maximum servicetemperature of the adhesive. A heat shrinkable sheet 8 (which mayoptionally be a heat recoverable fabric) coated with a heat-activatableadhesive 10 of the type described hereinbefore is then wrapped aroundthe weld region. It covers the weld region and overlaps the polymercoating 5 on either side thereof. The wraparound sheet is closed by apatch closure (not shown). Heat is then applied, e.g. by a gas torch, toshrink the sheet 8. This heat, together with the pipeline pre-heating,activates the adhesive 10. When the sheet 8 shrinks and the adhesive 10thereon initially contacts the preheated pipeline, the hot surfacesubstantially prevents the adhesive 10 from crystallizing. Additionalheat applied to shrink the sheet 8 raises the temperature of theadhesive 10 to make it fill and flow. Preferably the adhesive has aviscocity of about 1000 Pa.s. at 100° C., and a substantially lowerviscosity of about 500 Pa.s. at 110° C., and 300 Pa.s. at 120° C. Thusas the sheet shrinks it can force the adhesive into any surfaceirregularities and fill any gaps between the sheet and the pipeline. Thepost-heat shrink configuration is not illustrated.

Similarly the sheet could be applied over a damaged coated pipelinerather than at a join. Also it could be applied over a thermallyinsulated pipe such as a district heating pipe or a joint therebetween.

FIG. 2 shows an alternative embodiment. In this case the adhesive 10 isprovided on a tape 12. The pipeline is preheated as before, then thetape is helically wrapped around a metal pipeline 2 carrying oil (notillustrated). Adjacent turns of the tape overlap each other slightly.Heat applied to shrink the sleeve in combination with the preheat to thepipe activates the adhesive causing it to fill and flow. This ispossible despite the flowing oil in the pipeline, which acts as a heatsink.

In a similar way a helically wrapped tape could be applied to a polymercoated pipeline, or a joint between two such pipelines, e.g. to apipeline with a polyethylene coating, or to a district heating pipeline.

What is claimed is:
 1. A method of environmentally protecting apolymer-coated metal pipeline, or a joint between two such pipelineswhere the pipelines have been bared of polymer coating at the jointregion, the method comprising:(i) positioning a heat recoverable sheetwhich is coated on one surface thereof with a hot melt adhesivecomposition, such that the adhesive faces the pipeline, and such thatthe adhesive-coated sheet at least overlaps the polymer coating, theadhesive (a) comprising a mixture of 25 to 40 parts by weight of apolyethylene alkyl acrylate terpolymer containing maleic anhydride andhaving a melt flow index as determined according to ASTM D1238-70 of atleast 40, and 25 to 70 parts by weight of a polyethylene alkyl acrylatecopolymer having a melt flow index as determined according to ASTMD1238-70 of at least 40, and (b) having a maximum service temperature atwhich the adhesive maintains a bond to a substrate and shows no movementwhen subjected to a static shear creep force of 2.50 to 2.75 N/cm² ; and(ii) heating the pipeline or joint to a temperature of at most 40° C.above the maximum service temperature of the adhesive, said temperaturebeing sufficient to recover the sheet and to activate the adhesive.
 2. Amethod of covering a bare metal pipeline, a polymer coated pipeline, ora joint between such pipelines where the pipelines have been bared ofinsulation in the joint region, the method comprising(i) helicallywrapping a heat recoverable tape around the pipeline or insulation, thetape being coated on the inward facing surface with an adhesive which(a) comprises a mixture of 25 to 40 parts by weight of a polyethylenealkyl acrylate terpolymer containing maleic anhydride and having a meltflow index as determined according to ASTM D1238-70 of at least 40, and25 to 70 parts by weight of a polyethylene alkyl acrylate copolymerhaving a melt flow index as determined according to ASTM D1238-70 of atleast 40, and (b) has a maximum service temperature at which theadhesive maintains a bond to a substrate and shows no movement whensubjected to a static shear creep force of 2.50 to 2.75 N/cm² ; and (ii)heating the pipeline or joint to a temperature of at most 40° C. abovethe maximum service temperature of the adhesive, said temperature beingsufficient to recover the tape into close conformity with the pipeline,and to activate the adhesive.
 3. A method according to claim 1, whereinthe polymer coating on the metal pipeline is an extruded polyethylenecoating, a mil coating of sintered polyethylene, or a thermallyinsulating layer of polyurethane.
 4. A method according to claim 1 forcovering a joint between two pipelines pre-coated with a polymer coatingand bared of that coating in the joint region, wherein the sheet ispositioned to cover the bared joint region, and to overlap the polymercoating on either side of the joint region.
 5. A method according toclaim 1, wherein the terpolymer of the adhesive composition comprises(i) a polyethylene ethyl acrylate terpolymer, (ii) a polyethylene butylacrylate terpolymer, or (iii) a polyethylene ethyl acrylate terpolymerand a polyethylene butyl acrylate terpolymer.
 6. A method according toclaim 1, wherein the copolymer adhesive of the composition comprises (i)a polyethylene ethyl acrylate copolymer, (ii) a polyethylene butylacrylate copolymer, or (iii) a polyethylene ethyl acrylate copolymer anda polyethylene butyl acrylate copolymer.
 7. A method according to claim1, wherein the terpolymer of the adhesive composition comprises apolyethylene ethyl acrylate terpolymer and the copolymer comprises apolyethylene butyl acrylate copolymer.
 8. A method according to claim 1,wherein the heat recoverable sheet comprises a composite material thatis shrinkable by virtue of a shrinkable fiber component thereof.
 9. Amethod according to claim 3 wherein the polymer coating furthercomprises an outer jacket of polyethylene.
 10. A method according toclaim 2 wherein there is a polymer coating on the pipeline and thecoating is an extruded polyethylene coating, a mil coating of sinteredpolyethylene, or a thermally insulating layer of polyurethane.
 11. Amethod according to claim 2 for covering a joint between two pipelineswherein the tape is positioned to cover the bared joint region and tooverlap the polymer coating on either side of the joint region.
 12. Amethod according to claim 2, wherein the terpolymer of the adhesivecomposition comprises (i) a polyethylene ethyl acrylate terpolymer, (ii)a polyethylene butyl acrylate terpolymer, or (iii) a polyethylene ethylacrylate terpolymer and a polyethylene butyl acrylate terpolymer.
 13. Amethod according to claim 2, wherein the copolymer adhesive of thecomposition comprises (i) a polyethylene ethyl acrylate copolymer, (ii)a polyethylene butyl acrylate copolymer, or (iii) a polyethylene ethylacrylate copolymer and a polyethylene butyl acrylate copolymer.
 14. Amethod according to claim 2, wherein the terpolymer of the adhesivecomposition comprises a polyethylene ethyl acrylate terpolymer and thecopolymer comprises a polyethylene butyl acrylate copolymer.
 15. Amethod according to claim 2, wherein the heat recoverable tape comprisesa composite material that is shrinkable by virtue of a shrinkable fibercomponent thereof.
 16. A method according to claim 15, wherein thecomposite material comprises shrinkable fibers and a polyethylene matrixto which the adhesive composition is bonded.
 17. A method according toclaim 8, wherein the composite material comprises shrinkable fibers anda polyethylene matrix to which the adhesive composition is bonded.
 18. Apipeline or joint between pipelines having a heat recovered sheet orhelically wrapped tape adhered thereto by an adhesive (1) comprising amixture of (i) 25 to 40 parts by weight of a polyethylene alkyl acrylateterpolymer containing maleic anhydride and having a melt flow index asdetermined according to ASTM D1238-70 of at least 40, and (ii) 25 to 70parts by weight of a polyethylene alkyl acrylate copolymer having a meltflow index as determined according to ASTM D1238-70 of at least 40, and(2) having a maximum service temperature at which the adhesive maintainsa bond to a substrate and shows no movement when subjected to a staticshear creep force of 2.50 to 2.75 N/cm² ; wherein the sheet or tape wasrecovered and the adhesive was activated to bond it to the pipeline byheating the pipeline or joint to a temperature of at most 40° C. abovethe maximum service of the adhesive.